inheritance of ArrayAccess: Uncaught ErrorException: Collection::offsetExists($key)
Stefan Izdrail
Founder & Senior Architect · 2026-06-29
Title: Unraveling the Mystery of 'Collection::offsetExists' Error in Laravel
Introduction
Laravel is an open-source PHP framework that offers many features to simplify web application development and facilitate a seamless developer experience. One such feature is the "Illuminate\Support\Collection" class, which implements the ArrayAccess interface allowing you to treat collections as arrays. The offsetExists() method is used along with other methods like get(), put(), etc., to access elements within the Collection object. However, there are some scenarios where a PHP Fatal error might occur during inheritance of ArrayAccess. Let us dive into understanding this error and its solution.
The Error Message Breakdown:
First, let's analyze the error message - "During inheritance of ArrayAccess: Uncaught ErrorException: Return type of Illuminate\Support\Collection::offsetExists($key) should either be compatible with ArrayAccess::offsetExists(mixed $offset): bool, or the #[\ReturnTypeWillChange] attribute should be used to temporarily suppress the notice."
This error indicates that there is a mismatch between the return types declared for the offsetExists() method in the Illuminate\Support\Collection class and the one defined by the ArrayAccess interface. The original implementation of the interface demands that the offsetExists() method returns a boolean value, while it currently might be returning something else (incompatible type). This discrepancy leads to this fatal error during inheritance.
Solution: Updating ArrayAccess Implementation for Collection Class
To resolve this issue, you need to make sure to update the implementation of offsetExists() in your Collection class so that it fulfills the requirement of returning a boolean value. This implies that when you call the method with any key value and receive either true or false accordingly, the error will be fixed. Here's an example of how this might look:
class MyCollection extends ArrayAccess
{
public function offsetExists($key)
{
// Implement your logic to determine whether the specified key exists in the collection or not
return true; // Replace with actual implementation that returns boolean value
}
}
class MyCollection extends ArrayObject
{
public function offsetExists($key)
{
return parent::offsetExists($key); // Returning the method from parent class (ArrayObject) to maintain existing functionality
}
}